Identification and expression of forkhead box genes in the Chinese giant salamander Andrias davidianus

In the present study, 21 forkhead box (Fox) genes were identified in Andrias davidianus, including 13 full-length genes and eight partial sequences. Phylogenetic analysis showed that most were conserved in other investigated amphibians, whereas the Foxk1 gene was found exclusively in A. davidianus. Molecular evolution analysis indicated that most Fox genes underwent purifying selection, whereas two sites of the adFoxp4 gene showed positive selection and were located on the adFoxp4 protein surface. Expression profiles of all Fox genes identified were analysed in the hypothalamic-pituitary-gonad axis by reverse transcription-quantitative polymerase chain reaction. Eighteen genes exhibited sexually dimorphic expression (15 ovary-biased and three testis-biased genes), whereas two genes showed no difference between ovary and testis. Further investigation of 12 selected sexually dimorphic Fox genes showed changes in the expression profile of 11 genes in the ovary of larvae reared at high temperatures (28°C). The results of the present study provide information on Fox genes in an amphibian and suggest that they play key roles in sexual development and reproduction in A. davidianus.